Senate Minority Leader Mitch McConnell has until Thursday to defuse a standoff over filibuster changes, because Majority Leader Harry Reid indicated Tuesday that he is otherwise going to go “nuclear” on Republicans.

The Nevada Democrat on Tuesday outlined a package to his fellow party members that would eliminate at least one filibuster option for Republicans and place the burden of obstruction on the minority if they want to block other agenda items.

Reid, who has been in talks with the Kentucky Republican on a compromise plan, told reporters Tuesday afternoon that he hopes to have a bipartisan agreement on changes to the filibuster rule within the next 24 hours to 36 hours, but he emphasized that he was prepared to use the blunt object known as the “nuclear” or “constitutional” option, if needed.

Republican senators expressed optimism that there would be a path forward, but they left it to Reid and McConnell to work out the details.

“I think the two leaders are talking about it. I think they both probably talked about it at lunch, and my belief is they still have a little more talking to do, but we’ll see,” GOP Conference Vice Chairman Roy Blunt of Missouri said. “My guess would be that ... we need to decide this and probably will decide it pretty quickly.”

In the absence of a bipartisan agreement, Reid’s plan would eliminate filibusters on motions to proceed and require the minority to muster 41 votes to block other agenda items.

Reid’s ability to determine which items the Senate will take up has been hamstrung by the threat of filibusters on motions to proceed, which must be adopted for the Senate to formally debate most items. Traditionally, motions to proceed have been seen as the prerogative of the majority leader, but Republicans have objected to them more and more in recent years as a way of blocking or slowing down legislation.

Republicans counter that they have been forced to use the tactic because Reid too often uses a procedural device known as “filling the tree” to prevent them from offering amendments.

The package under discussion would strengthen Reid’s hand in agenda-setting and controlling time, but it may not make it much easier to actually pass bills.

Democrats have insisted they can change the rules at the beginning of a Congress with a simple majority, while Republicans have said the rules allow the minority to erect a 67-vote threshold for such alterations.

Sen. Tom Harkin, D-Iowa, said that while the package Reid presented would not go as far as he would like, it would represent an improvement over the status quo. Harkin has long pushed for a far-reaching proposal that would gradually decrease the number of votes needed to limit debate, or invoke cloture. Reid’s latest plan would set up a process that would require 41 votes in order to maintain a filibuster. Currently, the majority is required to find 60 affirmative votes to invoke cloture, but Reid’s plan would force 41 senators to show up to oppose the debate-limiting motion.

“To me that’s key that 41 would be required to maintain the filibuster,” Harkin said.

Unfortunately for Harkin and like-minded supporters, any negotiated agreement with McConnell is unlikely to include such a new burden on the minority.

Harkin and Sen. Jeff Merkley, D-Ore., are among those pushing Reid to use the simple-majority approach.

“Leader Reid has left open two paths to rules changes. While I’ve always thought that improving how the Senate works should be an area ripe for bipartisan agreement, it is clear at this point that the constitutional option would produce the strongest package and make the Senate more functional,” Merkley said. “We face big challenges, and we can’t tackle those challenges if we miss this rare opportunity to end the paralysis of the Senate.”

A 2011 push to make similar rules changes fell short when Reid and McConnell struck a gentlemen’s agreement that was intended to make the chamber work more smoothly. But last year, Reid said he had made a mistake on the handshake deal, and he accused Republicans of reneging on their promise to stop erecting roadblocks to most legislation.

Other pieces of Reid’s proposal have been more widely discussed. Reid’s plan would require no more than one cloture vote to get a bill to conference, as opposed to three. Harkin noted that Reid is favoring the idea of cutting down post-cloture debate time on judicial nominations from the 30 hours in current rules to just two hours.

A compromise plan floated by Sens. Carl Levin, D-Mich., John McCain, R-Ariz., and others would grant assurances to the minority party of a certain number of amendments.

Harkin expressed concern about any package that would guarantee amendment votes on a simple majority.

“What may happen as a compromise, what may happen in negotiations with Republicans, that may even make things worse,” he said. At the end of the day, however, Reid should have the votes to go ahead either way.

“Sen. Reid has the full backing of our caucus for whatever option he chooses,” Sen. Debbie Stabenow, D-Mich., said. She declined to put odds on the likelihood a deal is reached, saying that Democrats were prepared to proceed either way.

Reid wants to move ahead quickly in part because a disagreement about the rules package could mettle with advancing legislative priorities. Blunt said he did not expect a spending package of about $50.5 billion to assist recovery efforts from last year’s Superstorm Sandy could hit the floor until after the rules situation gets resolved. Blunt suggested both issues could see votes this week.